The invention relates to investment casting. More particularly, the invention relates to forming investment casting molds.
Investment casting is a commonly used technique for forming metallic components having complex geometries, especially hollow components, and is used in the fabrication of superalloy gas turbine engine components.
A well developed field exists regarding the investment casting of turbine engine parts such as blades and vanes. In an exemplary process, a mold is prepared having one or more mold cavities, each having a shape generally corresponding to the part to be cast. An exemplary process for preparing the mold involves the use of one or more wax patterns of the part. The patterns are formed by molding wax over ceramic cores generally corresponding to positives of the cooling passages within the parts. The patterns are mounted to a shelling fixture. Prior to mounting, the fixture may be prepared to receive the patterns. For example, the fixture may be dipped in wax to at least coat a base plate of the fixture. The wax patterns may be placed atop the wax coating on the base plate and wax welded thereto.
In a shelling process, a ceramic shell is formed around one or more such patterns such as by spraying and/or dipping a ceramic coating material over the fixtured patterns. The wax may be removed such as by melting in an autoclave. The shell may be further processed such as by trimming and sanding of a base surface to flatten the base surface. The shell may be fired to harden the shell. This leaves a mold comprising the shell having one or more part-defining compartments which, in turn, contain the ceramic core(s) defining the cooling passages. The shell may be seeded to define the crystal orientation of the ultimate part and placed with its base surface atop a chill plate in a casting furnace. Molten alloy may then be introduced to the mold to cast the part(s). Upon cooling and solidifying of the alloy, the shell and core may be mechanically and/or chemically removed from the molded part(s). The part(s) can then be machined and treated in one or more stages.
Nevertheless, there remains room for improvement in the art.